The long range objective of the research proposed in this application is to develop a new and more effective technique for measuring the relaxation and contraction of smooth muscle tissue in the trachea as it is affected by interaction with gasses and aerosols. Successful realization of this objective would have significant impact on pharmacological an toxicological studies involving response of the trachea to toxic gasses, airborne particulate pollutants, and liquid aerosols including drugs. The specific aim of the proposed research is to construct and test a new system to determine the response of isolated tracheas of small laboratory animals to test gasses and airborne particulates. A laboratory setup will be built to position an isolated trachea so that its outside surface can be bathed with a perfusion liquid held a constant temperature and bubbled with 5% CO2 and 95% O2. The epithelial or lumenal region of the trachea will be filled with air so that it can be ventilated with ozone gas, a liquid aerosol of methacholine, or airborne particulates derived from cotton dust. The response of the trachea to aerosols and gasses will be determined by measuring changes in the acoustical impedance of the trachea with respect to time. These data records will then be used in conjunction with signal processing algorithms to estimate changes in cross sectional area of the trachea, and the degree of the constriction of the tracheal smooth muscle.